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Wax Deposition And Control Biology Essay

This research carries out a critical review on previous work done on wax precipitation and deposition. However, the main focus of this work is on pour point. Several researches done on pour point were reviewed. Most of the work done by researchers was on pour point of oil/crude oil and methods of depression. Most of the depressant were successful but this depended on the crude oil content at most instances. The additive or depressant chemical structure also in some cases affected the outcome of the pour point depression. In some other cases, the molecular weights of the depressants affected the outcome of the pour point depression. With reference to concentration, when the concentrations of the depressants were reduced, an increase in pour point was realized. Conversely, when the concentration was increased, there was an increase in pour point depression.

CHAPTER 1

Introduction

Wax deposition and control continues to be a challenging problem in the oil and gas industry. This is because crude oil contains a mixture of waxes which precipitate out of solution at low temperature and pressure conditions. These waxes include normal alkanes, isomeric alkanes, alkyl cyclic compounds and alkyl aromatics. However, normal alkane or paraffin waxes are the major types present in crude hence, more widely studied. Paraffins with high molecular weight (C20 to C40) are the main causes of flow assurance problems in cold environments as regards wax formation and deposition, especially in subsea pipelines were the temperature could fall below 4°C. At high enough temperatures these high molecular weight waxes are dissolved in the crude and remain in solution. No formation or precipitation occurs at these temperatures but as the temperature drops below the wax appearance temperature (about 20 degree Celsius) wax is increasingly deposited along the wall of the pipeline and some paraffins dispersed in thecrude. However, if cooling continues, these dispersed paraffins gradually accumulate to form a white odourless, tasteless and waxy solid known as parrafin wax. In the petroleum industry, wax precipitation is undesirable because it may cause plugging of pipelines and process equipment (Galeana, 1996). The presence of these waxes thickens the crude oil and a continuous build up of wax could eventually clog the pipeline which could lead to a complete loss of production, resulting in shut down which would mean cost the company allot of money to tackle the problem.

Nowadays, there are many methods of wax mitigation. These include:

Pigging (involving a pig which mechanically scuffs wax from the walls of the pipelines).

Chemical solvent and dissolvers

Thermal techniques (which involves maintaining the crude oil temperature above the wax appearance temperature.

Wax inhibitors (like dispersants, surfactants, crystal modifiers and pour point depressants).

Wax precipitation could cause operational problems or eventually damage down hole and topside equipment although this occurs more frequently in subsea equipment as a result of very low ambient sea temperature. Because of the long chain waxes in crude oil, they are more difficult to control compared with those present in condensates. The wax appearance temperature could be as high as 50 degree Celsius for some oil and depends on the pressure, oil composition and the bubble point (Kelland, 2009). This high temperature as regards composition is usually as a result of the length of the paraffin chain present. Usually, the longer the chain the higher the melting point and hence, the more difficult it is to keep it in solution. Also with a high enough pressure, waxes could begin to form at temperatures as high as 50 degree Celsius or over. It is generally accepted that the conditions for wax formation or deposition are high pressure and low temperature. However, this implies that the lower the temperature the more likely it is for waxes to precipitate out of solution, since waxes could still be deposited at considerably higher temperatures.

There are several methods of wax control for the oil and gas industry, however, this review focuses on methods of pour point depression.

CHAPTER 2

LITERATURE REVIEW

3.1 Microbial treatment of waxy crude oils for mitigation of wax precipitation

(Etoumi A, 2007)

Etoumi, A (2007) carried out an experiment on microbial treatment of waxy crude oils for mitigation of wax precipitation. The materials used in the experiment are discussed briefly below.

3.1.1 Sarir crude oil

The Sarir crude oil was obtained from the Sarir field in eastern Libya. The oil is production is done through a 34-inch pipeline to the Tobrok terminal abd the distance between the field and the harbour is about 513.6 km. The oil from this field has a wax content of 13 wt.%, sulphur content of 0.133 wt.%, API gravity of 35.9, and Pour point temperature of 24 °C.

3.1.2 The microorganisms

Microbes were acquired from seawater sediment contaminated with hydrocarbon. The sediment samples were gotten from different locations of Alharka terminal in eastern Libya.

Enrichments culture experiments were done in batch experiments using a bioreactor containing 1.8 L of Enrichment Salts Medium (ESM). The salt medium was sterilized, and after sterilization, seawater sediment and crude oil were added to the sterilized ESM. The bioreactor was kept at a temperature of 37 °C. The incubation was 7 days.

The bacterial cultures isolated were PRCW E1, E2, B1, B2, A1, and A2. PRCW B1 was identified as Pseudomonas species and PRCW E1 and E2 were identified as filamentous type of Actinomyces species through microscopic examination.

Fig 2: Pure isolated cultures (Etoumi A, 2007)

Fig. 3 Growth curve of isolate PRCW E1. (Etoumi A, 2007)

Fig. 4: Growth curve of isolate PRCW B1. (Etoum

Table1: Specific growth rate and emulsification activity percent on kerosene of six isolates. (Etoumi A, 2007).

Isolates

Growth rate (h− 1)

E24 (%)

PRCW A1

0.0673

36

PRCW A2

0.1365

53

PRCW B1

0.2430

90

PRCW B2

0.0385

50

PRCW E1

0.1926

66

PRCW E2

0.0562

0

The result for the emulsification activity showed the isolates were able to emulsify n-hexadecane and Sarir crude oil which are immiscible hydrocarbons. The isolates produced considerable amount of bio-surfactant during growth on 0.5% (v/v) of n-hexadecane. Table 1 shows the specific growth rate and emulsification activity of six isolates with Kerosene. Also from the table PRCW B1 and PRCW E1 had emulsification activity percent (E24%) of 90 and 66% respectively. Etoumi A, 2007 compared these results with other organisms which produce bio-surfactant and suggested PRCW B1 may be a good candidate to inhibit paraffin deposition.

According to Lazar et al. (1999), bacteria control wax deposition by metabolising existing paraffin already precipitated, then partially digest the paraffin by breaking bonds between carbon atoms until the paraffin becomes more mobile. When this is done, the bacteria attacks other paraffin molecules. This means they do not really consume the oil.

Bio-surfactants formed by the bacteria also contribute to the breakdown of paraffins. Since the bacteria easily move from one location to another, this contributes to the effective break down of paraffins in crude oil.

According to Etoumi A, 2007, gas chromatographic experiment on untreated crude oil, 1 and 5% (v/v) crude oil with strains PRCW E1 and B1 showed a noticeable variation. The results show that the microbial breakdown of paraffinic hydrocarbon at 1% (v/v) was higher than that gotten at 5% (v/v).

Fig. 5: Gas chromatograms of Sarir crude oil, (A) untreated crude oil sample, (B) 1% (v/v) of treated crude oil with strain PRCW E1, (C) 5% (v/v) of treated crude oil with strain PRCW E1. (Etoumi A, 2007).

Fig. 6: Gas chromatograms of Sarir crude oil, (A) untreated crude oil sample, (B) 1% (v/v) of treated crude oil with strain PRCW B1, (C) 5% (v/v) of treated crude oil with strain PRCW B1. (Etoumi A, 2007).

WAT was measured after microbial treatment. Table 2 shows that the WAT decreased considerably after treatment with isolate PRCW E1. However, no significant change in WAT was observed when the crude was treated with isolate PRCW B1.

Table 2: Wax appearance temperature of crude oil before and after microbial treatment.

(Etoumi A, 2007).

Variable

Before treatment

Isolate PRCW E1

Isolate PRCW B1

WAT (°C)

50.94

38

51

3.2 INFLUENCE OF ALKANE CLASS-TYPES ON CRUDE OIL WAX CRYSTALLIZATION AND INHIBITORS EFFICIENCY

Garcı́a M, et al. (2000)

Garcia M, et al. carried out a research on the influence of alkane class-types on crude oil wax crystallization and inhibitors efficiency.

Seven samples of paraffinic crude oils were obtained from Venezuelan reservoirs. One commercial paraffin inhibitor (maleic anhydride α-olefin alkyl ester copolymer crystal modifier, identified as C-9) was used. (Etoumi A, 2007).

3.2.1 Enrichment (doping) of crude oils with paraffin concentrates

One gram of crude was heated to 60°C for 10mins until complete melting. Recorded quantities of C13-C20 and C20-C44 paraffin fractions were then added.

Lighter crude fractions (water and <200°C components) were separated by using atmospheric distillation. Asphaltenes were precipitated from the distillation residue with n-heptane. Maltenes (1.5 g) were deposited at the middle of the pre-column. Saturates were eluted in the forward flow mode, after a pre-heating delay of 5 min, using n-heptane at 5 ml/min as the mobile phase. The aromatics were collected using the same solvent, in the "back flush" mode at 10 ml/min. Resins were backflushed from the cyano columns with two successive elutions carried out at 10 ml/min with methylene chloride and chloroform/methanol 80:20 (v/v). Solvents from the separated fractions were evaporated in a rotary-evaporator, and the residues were placed in a vacuum oven kept at 60°C and 20 in. Hg, until constant weight was achieved.

n-paraffins were removed by inclusion of the saturate fraction in a 5 Šmolecular sieve, using dry i-octane as solvent in a 1.5:150 (wt/v) ratio. The sample was refluxed for 24 h, then the i-octane solution was decanted. The sieves were refluxed twice using the same solvent, over two periods of time of 30 min. The i-octane solutions were mixed and the cyclo+isoparaffins were obtained after solvent removal by distillation. Normal paraffins were recovered after destroying the sieves using hydrofluoric acid.

3.2.2 Characterization of the separated fractions

The purity of the saturates, aromatics, resins and asphaltenes fractions was verified by Thin Layer Chromatography with Flame Ionization Detection (TLC/FID. The >200°C residue and the n- and cyclo+isoparaffin fractions were characterized by High Temperature Simulated Distillation (HTSD).

3.2.3 Enrichment (doping) of crudes with cyclo+isoparaffin concentrates

Mixtures of crude oil and isolated cyclo+isoparaffins were prepared and kept to about 500 mg, being placed in 10 ml vials. The dopant concentration varied between 27 and 64 wt% of the above mass. Sample homogenization was carried out.

3.2.4 Crystallization changes in crudes and determination of the activity of a commercial paraffin inhibitor

Cloud point determination was used as a method to monitor the changes induced on the crude oils by the addition of the isolated paraffin fractions. The activity of a commercial paraffin modifier (C-9) was followed using the same cloud point measurement. Comparison was always referenced to the original crude, and the inhibitor activity value (cloud point depression) corresponds to the original crude oil cloud point minus the additivated crude cloud point.

3.2.5 Effects on the crude oils cloud point due to enrichment with light and heavy alkane concentrates

Previous studies show that multimodal crudes, with abundant <C24 components (Type II), were observed to improve their properties with the use of crystal.This is not the case for monomodal crude oils, with large concentration of >C24 alkanes (Type I), which were found to be insensitive to the action of these inhibitors. To further support these findings, synthetic blends were prepared using these two types of crudes. Additive refractory Type I crudes were enriched with light alkane concentrates (C13-C20) in an attempt to mimic the Type II crudes. Inhibitor sensitive Type II crudes were enriched with large paraffins (C20-C44) in order to mimic Type I crudes. Representative carbon number distributions for virgin crudes can be observed in the chromatograms (fig. 5). 

Fig. 5: Gas chromatograms of virgin crude oils:(a) crude M-4 (Type I); (b) crude G-8 (Type II). (Garcı́a M, et al. 2000)

Table 3: Activity of 2000 ppm of C-9 paraffin inhibitor on synthetic waxy crudes (values in parenthesis=wt% >C24). (Garcı́a M, et al. 2000).

Virgin crude

C-9 Activity (°C)a

Original

Synthetic blendb

Type Ic

M-4 (63)

0

3 (33)

N-9 (52)

−2

1 (33)

N-4 (77)

3

−6 (33)

N-6 (82)

1

−3 (33)

Type IId

G-8 (38)

13

5 (63)

O-7 (39)

10

−1 (63)

N-1 (31)

11

5 (63)

a - Cloud point depression respect to a control sample (without additive).

b - Dopant=paraffins C13-C20 (for Type I) and C20-C44 (for Type II).

c - Type I=monomodal crudes rich in >C24 alkanes.

d - Type II=multimodal crudes rich in <C24 alkanes.

After doping, additive refractory Type I crudes did not change the behavior to the presence of the C-9 crystal modifier. At the same time, doped Type II crudes drastically lost their response to this additive. These experiments support previous findings in the sense that significant proportions of heavy paraffins are found to be responsible for the inefficiency of crystal inhibitors. However, the addition of light paraffins to refractory Type I crudes did not improve the inhibitor performance upon them. This could be improved by increasing the concentration of light paraffins even more, but this is an unpractical and uneconomical approach.

3.2.6 Isolation and characterization of alkane concentrates from M-4 crude

The effect of whole alkane fractions on wax crystallization was investigated. Whole alkane fractions are commonly known as "saturates". In the case of saturates, there are three class-types: (I) the linear or normal alkanes; (II) the iso or branched alkanes; and (III) the cyclic alkanes, known also with the term naphthenes or cycloparaffins.

Alkane class-type fractions were separated from M-4 crude oil with the purpose of studying their effect on wax crystallization after doping the crude (M-4) with these fractions. Table 4 summarizes fraction yields for each stage during M-4 crude oil separation. Recovery of isolated fractions was 88.96 wt%. Losses (11.04 wt%) occurred during the molecular sieving adduction, more specifically, during the destruction of sieves andn-alkanes recovery.

Table 4: Fraction yields for M-4 crude oil separation (values in parenthesis indicate wt% based on the original crude oil), (Garcı́a M, et al. 2000).

Stage

Fraction

Yield (wt%)

Distillation (200°C)

Volatile fraction

28.01 (28.01)a

Distillation residue

71.99 (71.99)

Residue 200°C+deasphalation

Asphaltenes

0.26 (0.19)a

Maltenes

99.60 (71.71)

HPLC of >200°C maltenes

Saturates

77.61 (55.64)

Aromatics

20.53 (14.72)a

Resins

0.88 (0.63)a

Saturates inclusion

n-Paraffins

33.28 (18.51)a and b

Cyclo+isoparaffins

48.31 (26.89)a

Total

Recovered crude

(88.96)

a - Isolated fractions.

b - Noticed losses were observed during this step (expected: 28.75 wt%; found: 18.51 wt%).

Table 4 shows the carbon number distribution for the whole crude, the >200°C distillation residue and its cyclo+isoparaffins. Abundance of >C24 components for the residue was 78 wt%, higher than the value corresponding to the whole crude (63 wt%). Removal of the light end components (C5-C14) during distillation can account for this difference. The cyclo+isoparaffins fraction (26.89 wt% of the crude) was found to contain 84 wt% of C24+ components. These findings show that iso+cycloparaffins are, in average, larger in molecular mass than n-alkanes.

Table 5: Carbon number distribution of M-4 crude oil and its fractions by high temperature gas chromatography. (Garcı́a M, et al. 2000).

Fraction

Distribution

>C24 (wt%)

Whole crude

C5-C44

63

Residue >200°C

C14-C70

78

Cyclo+isoparaffins

C16-C60

84

Fig. 6 shows an expanded overlaid of the HTSD chromatograms corresponding to the saturates fraction from the whole crude and the one corresponding to its cyclo+isoparaffin fraction. Two types of signals can be distinguished: sharp peaks, attributed to the n- and isoparaffins, and an intense hump caused by the elution of the cyclic paraffins. The correct assignment of the n- and isoparaffins signals can be assessed with a detailed inspection of the overlaid chromatograms. It is evident that there is a retention time shift in the cyclo+isoparaffins fraction. In other words, one or more compounds from these classes are eluted between two intense peaks corresponding to the n-paraffins present in the whole saturates fraction. For a more accurate discrimination, high-resolution chromatographic columns and internal standards (i.e. n-paraffins) are required. Some authors use NMR-DEPT techniques (Nuclear Magnetic Resonance Distortionless Enhanced by Polarization Transfer) to clearly distinguish between CH2 and CH3/CH signals in the 13C NMR spectrum, which can help for the verification of fractions purity. Nevertheless this was beyond the purposes of the present study.

Fig.6: High temperature gas chromatograms of M-4 crude oil saturates and its cyclo+isoparaffins fraction. (Garcı́a M, et al. 2000).

3.2.7 Effect of crude oil enrichment with cyclo+isoparaffins fraction on the cloud point and wax inhibitor activity

Table 6 shows the cyclo+isoparaffins dosages used for the enrichment of the M-4 crude oil. Five "synthetic" crudes were prepared (entries 2-6), with a brown waxy solid appearance at room temperature, similar to that of the original oil (entry 1). From Fig. 6, it is possible to observe that there is no change in the cloud point value below a cyclo+isoparaffins concentration of ca. 40 wt%. The selective addition of branched and cyclic alkanes appears to impair the ordering of wax crystals in the present case. However, once a critical concentration is surpassed (ca. 45 wt%) an increase of the cloud point is observed for the prepared synthetic blends.

Table 6: Enrichment of M-4 crude with its isolated cyclo+isoparaffins fraction. (Garcı́a M, et al. 2000).

Entry

Crude aliquot (mg)

Cyclo+paraffin

Amount added (mg)

Wt%

1

500

0

27

2

462

50

34

3

419

100

41

4

345

150

49

5

407

200

51

6

253

250

64

a - Calculated concentration for the synthetic M-4 blend.

Fig. 6. Effect of cyclo+isoparaffins concentration on the cloud point of M-4 crude blends. (Garcı́a M, et al. 2000).

The activity of the commercial crystal modifier C-9 was also evaluated for the samples presented in Table 6, and the results are presented in Fig. 7. The inhibitor activity was measured as the cloud point of the oil blend minus the cloud point of the inhibitor treated sample. Negative activity values represent an increment of the cloud point after inhibitor addition, and the opposite is a better performance on the inhibitor activity (a decrease on the cloud point in the presence of this product). The zero point in the activity scale represents a null additive effect. The results indicate a slight decrease in the inhibitor activity up to 41 wt% of cyclo+isoparaffins, being the less affected the one for 8000 ppm inhibitor concentration. Beyond this point for paraffin concentration, the inhibitor activity starts to improve up to a value of four degrees. The improved inhibitor activity is probably due to an structural disorder introduced in the wax crystals when the concentration of cyclo+isoparaffins is greater than ca. 50 wt%.

Fig. 7. Activity of the commercial crystal modifier C-9. Experiments carried out with M-4 crude blended with its cyclo+isoparaffins fraction. âˆ- (Activity determined as crude oil blend cloud point minus additive treated crude blend cloud point). (Garcı́a M, et al. 2000).

3.3 Effect of asphaltenes on crude oil wax crystallization.

Pavel Kriz and Simon I. Andersen

Pavel Kriz and Simon I. Andersen carried out research on effect of asphaltenes on crude oil wax crystallization.

Asphaltene-in-toluene blends were first prepared. Then asphaltene-in-toluene mixtures were blended with the oil to attain the same concentration of asphaltene in all samples (0.1 wt %). The blending temperature which was found to be very important was 90 °C. If temperature was too low, the wax network was partly developed and the asphaltenes could not be fully applied inside.

For each asphaltene-toluene-oil blend, a control sample was prepared to get rid of the influence of solvent in successive experiments. This control sample was the crude oil diluted with the toluene. The other set was prepared in a similar fashion but the concentration of asphaltene was changed with fixed toluene concentration. The samples were prepared in concentration of 0.01 to 0.5 wt % of asphaltenes with toluene fixed at 28 wt %.

3.3.1 Wax Appearance Temperature (WAT) Measurement

WAT was calculated with the use of polarized light microscopy. The sample was heated to 80 °C and then cooled at a rate of 1 °C/min to 0 °C. This measurement was repeated three different times for each sample.

The experiment showed that the asphaltenes added to samples provided crystal sites for waxes.This occurred when asphaltene concentration was 0.05 wt % or higher. Conversely, at very low concentration (0.01%), WAT was unexpectedly high at almost 10 °C higher than the WAT for asphaltene-free oil. Pavel Kriz and Simon I. Andersen suggested that this behaviour was due to the fact that the asphaltenes were perfectly dispersed or almost dissolved and that they were affecting paraffins at the molecular level. With this, there are a number of likely crystal sites and they are simply reachable for paraffins because there are few asphaltenes per unit volume with more or less no risk of spatial interference. As asphaltene concentration is increased however, the surface area or number of possible sites increases. Hence, perhaps the WAT is increases also. This all comes to an end when the critical asphaltene concentration in the solution is reached. Here, the highest WAT is rattained and the asphaltene flocculation begins. This decreases the surface area severely.

3.3.2 Interaction of waxes with pour point depressants

Yin et al.

Yin et al. carried out an experiment on the interaction of waxes with pour point depressants. The influence of pour point depressant on wax precipitation at low temperature was investigated. The amount of precipitated wax from the paraffin solutions with and without pour point depressants were studied at different temperatures.

3.3.3 Material and Characteristic

Yin et al. made use of model oil which is composed of isooctane (a petroleum distillate with purity of 99.9%) and wax. The waxes which were supplied by Dallian Petrochemical Corporation were estimated to have melting points of 57.2 degree celcius and 67 degree Celsius respectively.

Fig. 8: composition of waxes as measured by gas chromatography. (Yin et al.)

The pour point depressants used in this study were the derivative of poly long alkyl methacrylate (CE) and the alkyl naphthalene copolymer (T801).

Yin et al. used two paraffin solutions to measure pour point. One of the solutions was made of 10 wt.% of 52.2 degree Celsius wax in isooctane, and the other on was made of 10 wt.% of 67 degree Celsius wax in isooctane. They were both heated to 80 degree Celsius for duration of 2 hours and then left to cool standing as the pour points of the solutions with and with no pour point depressants were measured by the Chinese national standard GB 510-1983 method.

The results arrived at by Yin et al. showed that pour point depressants do not prevent wax precipitation fully but only cause precipitation to occur at a lower temperature.

Since the pour point depressants are effective in different concentration range, the concentrations of both depressants were different for the experiment. Yin et al. pointed out that for effectiveness, the poly long alkyl methacrylate should be no less than 50 ppm and the alkyl naphthalene copolymer should remain in the range of 0.1 to 1.0%.

Samples

Composition

0 ppm

500 ppm CE

1%T801

Solution 1

10% wax1 in isooctane

12

11

<−5

Solution 2

10% wax2 in isooctane

22

9

<−5

Table 7: Composition and pour point of the paraffin solutions in degree Celsius. (Yin et al.)

From the table, CE proved to have very little or no effect on solution 1, however, T801 proved to be very effective in depressing the pour point of the solution. In solution 2 containing CE, a good level of pour point depression was noticed although, T801 still proved allot more effective having the same level of depression on solution 1 and 2.

Samples

0

0.2%

0.5%

1%

Pour point

12

<−5

<−5

<−5

Table 8: Pour point (in degrees Celsius) of solution 1 with different concentrations of T801 PPD. (Yin et al.)

From the table, T801 proved to have the same effect when different concentrations were used. This again shows that this pour point depressant is very effective even to concentration as little as 0.2%.

Samples

0

50 ppm

100 ppm

500 ppm

5000 ppm

Pour point

22

16

13

9

8

Table 9: Pour point (in degree Celsius) of solution 2 with different concentration of CE pour point depressant. (Yin et al.)

From the table, with increase in concentration of CE, the effectiveness increases. However, the pour point depressions are higher at 50 ppm to 500 ppm. When the concentration of CE is increased to 5000 ppm from 500 ppm, only a depression of 1 degree celsius is noticed. This means that this pour point depressant is not effective in large amounts. Also with the pour points arrived at, CE is still not as effective as T801 depressant.

3.4 Machado et al.

Machado et al. carried out an experiment to evaluate the effect of vinyl acetate content of ethylene-co-vinyl acetate (EVA) copolymers on viscosity and pour point of Brazilian crude oil. They also attempted to relate the crude oil WAT to the cloud point of the EVA as well as its performance as a pour point depressant.

3.4.1 Materials and Methods

Three samples of crude oil were used in the research. Two of the samples were obtained from Albacora field and the last was obtained from Badejo field in Brazil.

Table 10: Characterization data for EVA copolymers. (Machado et al.)

Copolymer

Vinyl acetate content(wt.%)

Molecular weight

MÌ„w

PD

EVA 20

20

10Ã-104

3

EVA 30

30

14Ã-104

3

EVA 40

40

10Ã-104

2

EVA 80

80

63Ã-104

3

Vinyl acetate content was determined by thermo gravimetric analyses (TGA) while molecular weight was determined by size exclusion chromatography (SEC).

Table 11: Crude oil characterization. (Machado et al.)

Crude oil

Shell paraffin contenta (%)

WATb (°C)

Pour point (°C)

Albacora 1

2.4

16.9

−8.0

Albacora 2

5.4

22.5

6.0

Badejo

7.2

19.5

18.0

The WAT was determined by differential scanning calorimetry (DSC), at 5 °C/min. The Pour points were determined by warming the crude oil which contained EVA.

Cloud points of the EVA solutions were taken to be the temperature, at which the crystals were completely dissolved. This was done by visual observation. The solvent media were cyclohexane, isooctane and dodecane.

For Albacora 2 crude oil, a reduction in pour point of 26 °C was attained. This occurred when 50 and 500 ppm of EVA 20 was added to the crude oil. However, the depressant lost its competence when the concentration was increased to 1000 and 5000 ppm.

Table 12: The influence of the EVA copolymers on the pour point of the Albacora 2 crude oil. (Machado et al.)

Additive concentration (ppm)

Pour point reduction (°C)

EVA 20

EVA 30

EVA 40

EVA 80

50

>26

22

10

0

500

>26

>26

>26

0

1000

22

-

-

-

5000

0

>26

>26

0

 EVA 80 did not show any efficiency as pour point depressant for this crude oil.

3.4.2 Cloud point of the EVA copolymers in organic solutions

Fig. 9: cloud points for copolymer solutions at 0.1 w/v%.

The solubility sequence for the three pure solvents was cyclohexane, isooctane, dodecane. The solubility of copolymer increased as the vinyl acetate content increased for cyclohexane and for ternary mixture. However, in most of the other solvent media, the solubility of EVA 30 was intermediate between EVA 20 and EVA 40.

Pour point for the systems: crude oil and crude oil/polymeric additive

Table shows the pour point results for pure crude oils and for the crude oil containing additive (EVA 20, EVA 30 and EVA 40).

Table 13: Pour point of the crude oils with and without additive

Additive

Pour point of the crude oil (°C)

Albacora 1

Badejo

-

−8

18

EVA 20

<−28

−21

EVA 30

<−28

−25

EVA 40

−25

−17

The depressants were more effective in reducing pour point of crude obtained from the Albacora 1 field. However, for the Badejo field, EVA 40 was less than EVA 20 and EVA 20 was less effective than EVA 30.

It was then concluded that EVA 30 was the most effective addictive. This goes to show that the performance of EVA copolymers as pour point depressant is largely dependent on the copolymer composition.

3.5 Synthesis of polymeric additives based on itaconic acid and their evaluation as pour point depressants for lube oil in relation to rheological flow properties

Sabagh A, et al. (2012) carried out an experiment on the synthesis of polymetric additives based on itaconic acid and their evaluation as pour point depressants for lube oil in relation to rheological flow properties.

Chemicals used include: Itaconic acid, hexadecyl alcohol, Octadecyl alcohol. Two linear saturated long chain alcohol blends NAFOL 20+A and NAFOL 1822 B were supplied from Condeu Chemical Company.

Table 14. Typical analysis of linear long-chain alcohol blends (NAFOL). (Sabagh A, et al. 2012)

Properties

NAFOL 20+A

NAFOL 1822 B

Composition, wt%

C16OH

0.9

0.2

C18OH

24.3

15.0

C20OH

24.4

14.8

C22OH

38.2

69.8

C24OH

9.9

0.2

C26OH

2.3

-

Average carbon number (calculated)

Cav = 20

Cav = 22

Density g/cm3 at 70 °C

0.803

0.802

Solidification point, °C

56-60

63-65

Ester no. mg KOH/g

9.9

0.16

Acid no. mg KOH/g

0.05

0.01

Water, wt%

0.06

0.04

Flash point, °C

208

204

Iodine no. mgL/100 mg

8.2

0.23

3.5.1 Lube oil composition

The lubrication oil was obtained from Suez Oil Processing Company (SOPC). The oil was used to assess the performance of synthesized polymeric additives. The normal paraffin content of the lubrication oil is determined by urea adduction. The oil and the n-paraffin fraction were then analysed using gas chromatography to determine the average molecular weight expressed as the average carbon number on the basis of carbon number distribution.

Table 15. Physicochemical properties of investigated lube oil. (Sabagh A, et al. 2012)

Test

Method

Result

Density@15 °C Kg/L

ASTM D1298

0.9083

Color

ASTM D1500

5.5

Pour point °C

ASTM D97

15

Flash point °C (PMC)

ASTM D93

203

Kinematic viscosity@ 40 °C CST

ASTM D445

243.59

Kinematic viscosity@ 100 °C CST

ASTM D445

18.94

Viscosity index

ASTM D445

87

Saybolt viscosity@ 100 °F SUS

ASTM D445

96.8

X-ray (sulfur) wt%

ASTM D4294

1.084

n-paraffins, wt%

GLC

62.27

Iso-paraffin, wt%

GLC

4.12

Total paraffins content, wt%

Urea adduct

66.39

Average carbon number (n)

GLC

28.56

Table 16: Characteristization of the synthesized polymeric additives. (Sabagh A, et al. 2012)

Additive designation

Composition

Molar ratio alkyl itaconate-styrene (%)

Average side carbon length (Cav)

M.wt.

Poly dispersity index

PPD 1

PPD 2

PPD 3

Poly (hexadecyl itaconate-styrene)

25:75

50:50

75:25

16

40313

45411

38513

1.68

1.70

1.50

PPD 4

PPD 5

PPD 6

Poly (octadecyl itaconate-styrene)

25:75

50:50

75:25

18

40933

48415

41513

1.70

1.72

1.62

PPD 7

PPD 8

PPD 9

Poly (NAFOL 20+A itaconate- styrene)

25:75

50:50

75:25

20

58298

35026

28858

1.57

1.50

1.31

PPD 10

PPD 11

PPD 12

Poly (NAFOL 1822 B itaconate styrene)

25:75

50:50

75:25

22

60096

37710

30512

1.58

1.55

1.20

3.5.2 Characterization of copolymers

The structures of the synthesized mono-esters alkyl itaconate and copolymers with styrene were established using Infrared (IR) spectroscopic analysis. The infrared spectra were calculated by using the model Genesis series (USA) infrared spectro-photometer adopting KBr technique. The structure of the prepared mono-esters alkyl itaconate and copolymers with styrene was found using nuclear Magnetic Resonance Spectroscopic analysis. Copolymers of the different alkyl itaconate with styrene were then abbreviated as PPD1-PPD3 (C16), PPD4-PPD6 (C18), PPD7-PPD9 (C20), PPD10-PPD12 (C22). The esterification and copolymerization are shown in fig 10.

fig 10. esterification and copolymerization (Sabagh A, et al. 2012)

3.5.3 Pour point measurement (ASTM D 97-96)

The solutions of oil soluble samples PPD1-PPD12 in toluene were prepared using the ASTM, D97-96 method. PPD solutions were introduced into the lubrication oil and examined as pour point depressants at varying concentrations (250, 500,1000,1500,2000 and 3000 ppm) of. Pour point was set at 2.8 °C above the actual temperature which the oil solidifies. 

 Influence of pendant chain length of the various copolymers on their effectiveness in terms of pour point depression

The different alkyl chains were effective on the pour point depression of lube oil. However, PPD1-3 C16 was more effective than PPD4-6 C18, PPD4-6 C18 was more effective than PPD7-9 C20, and PPD7-9 C20 was more effective than PPD10-12 C22. The results in table 16 shows that the depressant efficiency declines as the alkyl chain length from C16 to C22 is increased. C16 itaconate-styrene attained the best flow improver to the extent of PP2000 ppm = −15 °C at molar ratio 50%:50% (PPD2). The results show that reducing the alkyl chain length from C22 to C16 improves the interaction between the alkyl chain of the copolymer and paraffin in the lubrication oil. This mean inhibition of wax crystal deposition could be obtained.

Table 16 Effect of the polymeric additives on the flowability of lube oil. (Sabagh A, et al. 2012).

Lube oil

Additive design

Additive concentration, ppm

Nil

250

500

1000

1500

2000

3000

pp

Δpp

pp

Δpp

pp

Δpp

pp

Δpp

pp

Δpp

pp

Δpp

PPD 1

15

12

3

12

3

0

15

−3

18

−9

24

−12

27

PPD 2

15

12

3

3

12

0

15

−9

24

−18

33

−18

33

PPD 3

15

12

3

12

3

3

12

0

15

−6

21

−9

24

PPD 4

15

12

3

12

3

0

15

−6

21

−9

24

−12

27

PPD 5

15

12

3

0

15

−3

18

−9

24

−15

30

−15

30

PPD 6

15

12

3

12

3

6

9

0

15

−6

21

−9

24

PPD 7

15

12

3

12

3

6

9

0

15

−6

21

−9

24

PPD 8

15

12

3

9

6

3

12

−3

18

−12

27

−12

27

PPD 9

15

12

3

9

6

6

9

3

12

0

15

−6

21

PPD 10

15

15

0

12

3

3

12

−3

18

−6

21

−9

24

PPD 11

15

15

0

12

3

3

12

−3

18

−6

21

−9

24

PPD 12

15

15

0

12

3

9

6

6

9

0

15

−3

18

Influence of the average molecular weights of the various investigated copolymers on their effectiveness in terms as pour point depression

The synthesized polymers (PPD1-PPD12) were examined and their average molecular weights and polydispersity were calculated by GPC analysis. The result proved that the molecular weights of the depressants were different beginning from 28,858 to 60,096 and that the best efficiency is attained at the range of 40,313 to 48,415 (PPD1, PPD2, PPD4, PPD5, PPD6). The results also show that PPD2 and PPD5, had the highest poly dispersity index and brought about the best pour point depression. The least pour point depressions were attained by PPD9 and PPD12, having the lowest polydispersity.

When the concentration of the additives was increased, increased action was attained and this had a huge depression on pour point was achieved. It was also noticed that the pour point continually reduced as the depressant concentration increased to 2000 ppm. Normally, with a lower concentration of depressant side way growth of the crystal may be somewhat hindered and the crystal growth would be slower. This nevertheless does not mean deposition would not still occur. At considerably high concentrations of depressants, the side way growth becomes more difficult for the wax crystals.

3.6 Polymethacrylates: Pour point depressants in diesel oil

Soldi R, et al (2007) carried out an experiment using methyl methacrylate as pour point depressants in diesel oil.

The methyl methacrylate (MMA) used was washed severally times with an aqueous solution of NaOH and washed again distilled water. This was dried with anhydrous magnesium sulphate and then distilled.

3.6.1 Synthesis of the methacrylic monomers

In a round-bottom flask connected to a distillation microsystem, octadecyl alcohol and methyl methacrylate were added (1:4 molar ratio), as well as p-toluenesulfonic acid (PTSA) (0.5 mol%), and hydroquinone (3% w/w, in relation to MMA).

The flask containing the reactional medium was heated to 90 °C, and kept under magnetic stirring by 24 h. The temperature was, then, raised gradually until the end of the distillation.

The excess of residual methyl methacrylate was removed through distillation at a reduced pressure and the octadecyl methacrylate (ODMA), was purified in methanol.

The same experimental conditions were used in the synthesis of tetradecyl methacrylate (TDMA) and of hexadecyl methacrylate (HDMA), by using the, respectively, fatty alcohol.

3.6.2 Synthesis of methacrylic copolymers

In a two-necked round-bottomed flask the methyl methacrylate and octadecyl methacrylate were mixed in molar ratio of 50:50. Polymerization was done in a toluene solution. This reaction was carried out at 70 °C for 17 hours under nitrogen atmosphere and magnetic stirring. The toluene was then evaporated under low pressure.

After the pour point of diesel oil was established, the influence of quantity of solvent (toluene) and the effect of the fatty monomers on the pour point of the oil was examined. It was seen that the presence of different amounts of toluene in the oil had no effect on its pour point. The quantities of monomers used which were higher than the amount of polymeric additive also had no effect on the pour point. Hence, there was the need for a polymeric backbone so as to achieve the required effect of these type of pour point depressant.

To evaluate performance of the different polymeric compounds obtained, a sample of diesel oil called "type D" was used. This oil has a pour point of 0 °C.

For each of the methacrylic polymer tested in the type D diesel oil, at two pour point evaluation were done using additive concentration of 50 ppm.

Table 17: Results of pour point of type D diesel oil (pour point = 0 °C) treated with 50 ppm of methacrylic copolymers of different compositions. (Soldi R, et al 2007).

Methacrylic additives

Composition in the copolymer

Pour point (°C)

Reduction observed (°C)

Alkyl methacrylate (mol%)

Methyl methacrylate (mol%)

PODMMA73

67

33

−22

22

PODMMA55

42

58

−18

18

PODMMA37

26

74

−10

10

PHDMMA73

66

34

−18

18

PHDMMA55

53

47

−13

13

PHDMMA37

26

74

−7

7

PTDMMA73

67

33

−10

10

PTDMMA55

52

48

−10

10

PTDMMA37

29

71

−10

10

{Tetradecyl methacrylate copolymers (PTDMMA), poly(octadecyl methacrylate-co-methyl methacrylate) (PODMMA), hexadecyl methacrylate copolymers (PHDMMA)}.

When studying the structure-activity relation in polymeric additives for oil and its products it is common to find in the literature a given composition beyond which an increase in the proportion of active groups does not affect the performance of the additive anymore, to the contrary it could make it worse.

From the table, in the case of the octadecyl group, for the same size of hydrocarbon group, increasing the amount of these groups improved the performance of the additive. This is because the long hydrocarbon paraffins have a tendency to interact with the polymer alkyl groups which act as crystallization nuclei. This means that the larger the numbers of crystallization nuclei , the less free paraffin to obstruct fluidity with the decreasing temperature and as a result, pour point will be less. On the other hand, if the quantity of long groups is too high, they could get in the way of crystallization on the polymer chain.

In the areas where a small concentration of the methacrylic additive synthesized shows low pour point values, there is a probability that much smaller doses could be used for a considerable decrease in the pour point of type D diesel oil.

3.7 Improving cold flow properties of canola-based biodiesel

Chastek T, (2011) carried out an experiment on improving the cold flow properties of canola based biodiesel.

3.7.1 Materials

The Canola-based biodiesel was acquired from Inland Empire Oilseed LLC (denoted as Biodiesel A). Methyl oleate (70%) (denoted as Biodiesel B), methyl stearate (≥96%), methyl palmitate (≥96%), dioctyl phthalate (DOP, 99%), and anisole (99.7) were obtained from Sigma-Aldrich. Tetrahydrofuran (THF) (99.5%), butanol (99.9%), and pentane (>99%) were obtained from JT Baker. Acetone (99.99%) was obtained from VWR. Gas chromatography was used to measure the chemical compositions of Biodiesel A and Biodiesel B.

Table 18. Composition of biodiesel samples. (Chastek T, 2011).

Melting point, pure, °C

% in biodiesel Aa

% in

biodiesel Ba

Methyl eicosanoate

20:0

46.4

0.6

0.0

Methyl stearate

18:0

37.7

1.8

1.0

Methyl palmitate

16:0

28.5

3.8

4.7

Methyl palmitoleate

16:1

−3.0

0.2

5.3

Methyl gadoleate

20:1

−7.8

1.2

0.0

Methyl oleate

18:1

−20.2

65.2

79.7

Methyl linoleate

18:2

−35

19.1

9.4

Methyl linolenate

18:3

−52

8.0

0.0

% in biodiesel is the weight percent based on peak area of GC measurement.

Polymers were dispersed in Biodiesel A and B through vortex mixing and heating. For polymers supplied as solutions in toluene, the toluene was removed using vacuum heating prior to combining with biodiesel.

Cloud points, pour points, and low temperature filterability points were noticed upon cooling samples (<0.3 °C/min). The samples were directly immersed in the temperature bath. All samples presented in Table below were cooled at the same time for uniformity so that relative performance of the different solvents and additives could be correctly compared. Also some samples were mixed (magnetic stir bar, 300 RPM) as they cooled just about 3 °C below the cloud point. Additional cooling of the samples was done without stirring.

Table 19: Cold flow properties of biodiesel with added polymers. (Chastek T, 2011).

Weight percenta

Cloud point, °C biodiesel A

Pour pointb, °C biodiesel A

Low temperature filterability pointc, °C biodiesel A

Cloud point, °C biodiesel B

Pour pointb, °C biodiesel B

Low temperature filterability pointc, °C biodiesel B

Biodiesel Ad

-

−12

−16

-

-

-

-

Biodiesel Be

-

-

-

-

−22

−24

-

poly(octyl methacrylate)

1.0

−12

−19

-

−17

−21

-

poly(decyl methacrylate)

1.0

−12

−19

-

−17

−22

-

poly(lauryl methacrylate)f

1.0

−12

−46(−46)

−27(−44)

−22

−42

−42

poly(lauryl methacrylate)g

0.14

−12

−28(−43)

−27(−27)

−22

−27

−24

poly(lauryl methacrylate)g

0.50

−12

−43(−44)

−28(−43)

−22

−35

−24 (−28)

poly(lauryl methacrylate)g

1.0

−12

−44(−45)

−27(−38)

−24

−37.5

−27 (−32)

poly(lauryl methacrylate)g

2.0

−12

−41(−43)

−27(−43)

−24

−35

−35

poly(lauryl methacrylate)g

3.9

−12

−43(−43)

−27(−43)

−24

−33

−35

PLMA-b-PMMA

1.0

−12

−41(−47)

−27(−43)

−21

−39.5

−29.5

PLMA-r-PMMA

1.0

−12

−23

-

−22

−42

−29.5

poly(vinyl laurate)

1.0

−12

−22

−22

−25.5

−29.5

−28.5

poly(hexadecyl methacrylate)

1.0

−12

−20

-

−7.5

−24

-

PODMA-b-PMMA 38K

0.97

−12

−12

-

−3

−21

-

PODMA-b-PMMA 63K

1.0

−12

−17

-

−3

−24

-

poly(octadecyl vinyl ether-co-maleic anhydride)

1.0

−12

−19

-

−1

−24

-

poly(ethylene-co-vinyl acetate), 18% vinyl acetate

1.0

−12

−42h(−27)

−22(−27)

5

−24

-

poly(ethylene-co-vinyl acetate), 50% vinyl acetate

1.0

−13.5

−14

-

−22

−24

-

a) Weight percent of polymer in methyl oleate.

b) The pour point values in parentheses correspond to stirred samples.

c) The low temperature filterability point values are only reported if they are notably lower than the pour point of the unmodified Biodiesel; the values in parentheses correspond to stirred samples.

d)Canola-based biodiesel.

e) A commercially available technical grade methyl oleate (70% purity, Aldrich) was measured for comparison to canola-based biodiesel.

f) Synthesized via ATRP, 13.5 kg/mol.

g) Purchased from Scientific Polymer Products, 250 kg/mol.

h) The viscous composition of the unstirred sample made assignment of PP unclear. Additional measurements were made on poly(isobutyl methacrylate), poly(benzyl methacrylate), poly(hexyl methacrylate), and poly(styrene). However, initial results showed no lowering of the PP or LTFP temperatures. (Chastek T, 2011).

Measuring pour point temperature provides a rather clear understanding of what polymers promote the cold flow properties of biodiesel. The basic finding was that the poly (lauryl methacrylate) and its copolymers considerably reduced the pour point of biodiesel. The other polymers showed negligible improvement. The polymers performances and efficiencies were linked to chemical structure. For poly (decyl methacrylate) and poly(hexadecyl methacrylate), they had minimal impact on pour point in spite of their chemical similarity to poly(lauryl methacrylate).

Also, the poly(lauryl methacrylate) copolymers lowered the pour point temperature, but the effect was not as considerable as the poly(lauryl methacrylate) monomer. From these results, the chemical structure and properties of lauryl methacrylate monomer give it high affinity to the crystallizing saturated methyl esters. As a result of this affinity, poly(lauryl methacrylate) can have an effect on the saturated methyl ester crystal size more than any of the other additives would have.

The impact of poly(lauryl methacrylate) (250 kg/mol) concentration was also examined. At 0.14%, the poly(lauryl methacrylate) had a reduced impact on pour point with respect to higher concentrations. It was noted that a 1% additive concentration may be too much for biodiesel treat rate as allot of producers of pour point depressants (PPDs) suggest 1000 ppm treat rates. So it is likely that low concentrations could perform better as PPDs often have poor cold flow properties.

3.8 Effect of wax inhibitors on pour point and rheological properties of Iranian waxy crude oil

Taraneh J, et al. (2008) carried out an experiment on effect of wax inhibitors on pour point and rheological properties of iranian waxy crude oil.

Five samples were provided from the Iranian waxy crude oils (crude-1 to crude-5) to assess the performance of flow improvers. The physical properties and rheological behaviour of the crude oils are provided in tables.

Table 20. Physical characteristics of crude oils. (Taraneh J, et al. 2008)

Specification

Crude-1

Crude-2

Crude-3

Crude-4

Crude-5

Methods

Specific gravity at 15.56/15.56 °C

0.8503

0.8661

0.8846

0.8944

0.9033

ASTM D-4052

API

34.9

31.9

28.5

26.7

25.1

ASTM D-4053

Kinematic viscosity at 40 °C C.St.

7.828

10.959

12.525

14.689

15.125

ASTM D-445

Kinematic viscosity at 100 °C C.St.

2.751

3.852

4.656

6.136

8.698

ASTM D-446

Pour point (°C)

26

20

17

14

8

ASTM D-97

Asphaltene content (wt.%)

0.3

1.5

2.8

4.7

7.8

IP-143

Wax content (wt.%)

13.1

11.2

9.7

7.4

5.2

BP-237

Table 21. Viscosity (mPa s) of crude oils. (Taraneh J, et al. 2008)

Type

Shear rate, s− 1

40 °C

20 °C

15 °C

10 °C

5 °C

Crude-1

70

14.0

275

580

920

1680

100

14.0

223

460

750

1189

300

13.8

125

265

365

526

Crude-2

70

14.8

301

615

982

1850

100

14.5

250

505

810

1308

300

14.3

155

303

385

675

Crude-3

70

15.5

352

690

1021

2025

100

15.1

320

580

860

1560

300

15.0

210

398

420

715

Crude-4

70

15.9

401

750

1562

2950

100

16.1

390

640

1050

2010

300

16.8

280

480

490

886

Crude-5

70

16.9

489

910

2130

3852

100

17.0

550

850

1680

2541

300

17.9

405

620

630

985

Four different types of commercial ethylene-vinyl acetate copolymer (EVA) were used as flow improvers.

Table 22. Characteristics of polymers used. (Taraneh J, et al. 2008)

Characteristics of polymers

EVA20

EVA40

EVA80

EVA32

Mw (104)

10

10

63

5.5

Composition (VA content) (wt.%)

20

40

80

32

The waxy crude oils used have different asphaltene contents. The asphaltene content of crude 5 was (7.8%) more than the asphaltene content of crude 1 (0.3%). The wax content of these crude oils also varied from 5.2% to 13.1% which affected pour point behaviours.

Effect of molecular weight of flow improver and asphaltene content of crude oil on pour point of the Iranian waxy crude oil

Table 23. Viscosity (mPa s) of crude oils at a shear rate of 100 s− 1 treated with flow improver EVA80 and EVA32 in different concentrations

Type

Concentration (EVA80), ppm

40 °C

20 °C

15 °C

10 °C

5 °C

Concentration (EVA32), ppm

40 °C

20 °C

15 °C

10 °C

5 °C

Crude-1

500

10

39

155

415

760

500

13

44

368

691

992

1000

8

30

120

360

710

1000

10

38

292

612

874

2000

2

25

98

310

680

2000

5

34

221

538

842

Crude-2

500

14

42

180

440

780

500

12

42

352

656

910

1000

12

36

140

380

740

1000

9

36

268

584

855

2000

7

30

110

340

715

2000

4

30

197

502

810

Crude-3

500

16

45

210

492

810

500

11

40

302

602

895

1000

14

40

180

410

780

1000

9

32

210

554

802

2000

9

35

150

385

730

2000

4

24

170

471

780

Crude-4

500

16

47

280

530

865

500

11

38

250

590

820

1000

15

42

225

485

812

1000

9

32

190

510

780

2000

9

38

186

427

785

2000

3

24

150

410

720

Crude-5

500

18

52

352

587

912

500

9

38

170

440

750

1000

16

48

286

512

868

1000

7

32

110

350

710

2000

10

43

227

487

802

2000

1

25

90

310

683

From the result on viscosity reduction of the crude oil with different concentration of flow improver dissolved in cyclohexane at a shear rate of 100 s− 1, the high molecular weight EVA80 has a good efficiency for crude 1 which has little asphaltene (0.3%). On the other hand, lower molecular weight EVA32 is the best flow improver for crude 5 with high asphaltene content (7.8%).

It was also noticed that the high molecular weight flow improver shows better effectiveness on pour point of crude oil with low asphaltene content. In addition, the lower molecular weight flow improver shows a better competence for crude oil with higher asphaltene content.

Table 24. Effect of different flow improvers on the pour point of the crude oils with different concentrations. (Taraneh J, et al. 2008)

Type

Concentration, ppm

EVA80

EVA20

EVA40

EVA32

Crude-1

500

15

19

21

20

1000

5

13

16

14

2000

− 2

9

13

10

Crude-2

500

14

15

16

16

1000

7

8

10

10

2000

1

4

7

6

Crude-3

500

12

9

12

10

1000

7

3

6

5

2000

2

− 1

3

1

Crude-4

500

9

7

10

7


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